The point of a retained sample is to be able to reproduce that decision, not to keep a souvenir
Retained sample management involves exactly four decisions: whether to retain, which unit to retain, how to store it, and how long to keep it. All four judgements point at the same objective. When someone later questions the report, can the laboratory produce a physical item whose condition matches the object that was actually tested? A retained sample that cannot do that occupies shelf space and consumes management effort, and then turns out to be useless when a dispute finally arrives.
What ISO/IEC 17025 asks for in terms of sample handling can be summarised like this: while a sample is under laboratory control its condition must be controlled and traceable, and disposal must follow a rule, be recorded and be authorised. What exactly to retain, and for how long, is not fixed for you by the standard. The laboratory has to define it in its own management system and make it clear to the client in the service agreement. That is why retention policies differ so much between laboratories, and why the question "do you retain a sample for this item, and until when" belongs in the conversation before the order is placed.
Decision one: does this item need a retained sample at all
More is not better. Storage capacity is finite, and samples containing batteries, volatile materials or biologically sourced materials carry management risk of their own. Deciding by the nature of the test is far more reliable than deciding by how expensive the sample was.
| Nature of the test | Need for retention | Reasoning |
|---|---|---|
| Non-destructive testing (appearance, dimensional items, some functional verification) | Retention recommended | Sample condition is essentially unchanged, so a retest remains comparable |
| Destructive testing (strength, durability, material failure types) | Retain the tested remains, and wherever possible an untested unit from the same batch | The remains only prove the test happened; only an untested unit has retest value |
| Sterile barrier system related work (package integrity, seal performance) | An unopened unit must be retained | The act of opening changes the object under test, so an opened unit cannot support a retest |
| Extraction and preparation for biological evaluation | Retain the original sample together with the preparation records | Preparation is irreversible, so the only route back is records plus the original sample |
| Electrical safety and electromagnetic compatibility | Retain the complete unit, or key components with full identification | Disputes cluster around configuration and condition, so physical verification of configuration is needed |
The row people most often take for granted is destructive testing. The common assumption is "it is gone once it has been tested, so keeping a fragment is a formality". In reality the evidential value of the remains and of an untested unit is completely different. The remains answer "was the test performed, and is the failure mode consistent". An untested unit answers "what happens if we measure it again". The second question is the one actually asked when a dispute breaks out. So sample quantities have to be prepared at submission time as test quantity plus retention quantity together, not worked out afterwards from whatever happens to be left.
Decision two: which unit to keep, and how to bind it to the report
Every retained sample needs its own dedicated identification number, and that number has to be traceable in both directions to the report number, the submission record, the batch information and the test records. A retained sample without two-way traceability is a physical object on a shelf attached to a broken evidence chain.
The information that has to be fixed alongside it includes: the batch or production identification of the sample, a description of its condition on receipt, whether it has been tested and which tests it went through, the start date of retention, and who is authorised to dispose of it. This information belongs both on a label attached to the sample and in the system record. Record it in only one place and the sample is easy to lose track of the moment it is moved.
One point gets overlooked routinely: the condition description has to record the condition on receipt, not the condition the item should have had when it left the factory. Transit scuffs, deformed packaging, missing accessories, all of these get raised when a dispute starts, and recording them honestly on receipt actually protects the laboratory and the client alike. The submission and condition confirmation requirements that go with this can be prepared in advance against the testing requirements.
Decision three: storage conditions, and which mistake voids the retained sample outright
| Management dimension | Baseline requirement | What goes wrong if it is missed |
|---|---|---|
| Environment | Ambient, dry, away from light, clear of heat sources and direct sunlight, without pronounced temperature and humidity swings | Polymer parts age, metal parts corrode, and retest data is no longer comparable with the original data |
| Chemical segregation | Not stored with detergents, solvents or volatile chemicals | Adsorption or migration into the material contaminates biological and materials retests |
| Packaging | Keep the original packaging condition as received; sterile barrier system units must not be transferred or repackaged | The object under test itself has been altered, so a retest is meaningless |
| Identification | Number, report number, retention start and end, disposal authoriser, complete and not prone to falling off | A lost label means a void sample: the item is still there but cannot be proved to be the one |
| Physical segregation | Stored in an area separate from samples awaiting test, samples for return and samples awaiting disposal | The wrong unit gets picked up, and the data does not match the actual sample |
| Records | Movements in and out, transfers and environmental excursions all leave a trace | No way to explain what the sample went through in storage, and the evidence weakens |
The packaging row needs unpacking. Following the logic of ISO 11607, the packaging of a sterile barrier system is itself the object being evaluated. Its seal performance, material integrity and opening characteristics all rest on the premise that the packaging has not been disturbed. If a retained unit is pulled out of its original carton and stored loose to save space, or the outer packaging is stripped off and only the inner packaging kept, that unit has already lost its value for any retest related to package integrity. By the same logic, stacking arrangement and stack height put sustained stress on the seals, so samples of this kind should not sit at the bottom of the rack. Preparation and retention practice for these samples can be checked against the sample condition requirements set out under packaging testing.
Decision four: how to set the retention period
A retention period should not be plucked out of the air, and it should not be copied blindly from someone else's policy. Several factors set it together:
- A retention period explicitly agreed with the client in the contract; where there is a written agreement, the agreement governs
- The intended use of the report. A report going into a registration dossier can be looked back at over a much longer window than one supporting internal verification
- The stability of the sample itself. The retention period should not outlast the period over which the sample still has retest value; past that point all you are storing is a shelf of degraded objects
- Storage capacity and safety constraints. Samples containing batteries, pressurised parts or biologically sourced materials carry extra management cost and risk
- Traceability windows expected by the receiving party or by industry practice
The working rule is to take the intersection: not shorter than the period over which the report may be revisited, and not longer than the period over which the sample still has retest value. If the two conflict, for example when stability is poor but the traceability window is long, that has to be said out loud at the ordering stage, and the evidence gap should be filled another way, with retained photographic records, retained raw data, or retained untested units from the same batch, rather than by stubbornly keeping an item that stopped being usable a long time ago. Judging the stability of the sample itself follows the same reasoning as the evaluation logic behind shelf life and stability.
When the client comes back asking for a retest, can the retained sample carry it
This is where the disputes concentrate. Different retest requests depend on the retained sample to completely different degrees.
| Retest request | Can the retained sample carry it | Basis for the judgement |
|---|---|---|
| Check whether report data was transcribed incorrectly | No retained sample needed | Checking the raw records and the raw data files is enough |
| Confirm the test really was run to the method | Remains plus records can carry it | Whether the failure mode of the remains fits the method description and the test records |
| Measure the same parameter again | Depends on whether the sample has aged or drifted in condition | Polymer parts, battery-containing units and sterile barrier units carry clearly higher risk |
| Re-decide against a different method or a different limit | Generally cannot use the retained sample | This is a new testing engagement and fresh samples should be submitted |
| Data dispute with the receiving party | High value | Can be used for witnessed retesting or interlaboratory comparison |
One point of interpretation has to be stated plainly: data obtained from retesting a retained sample only describes how that retained sample behaves in its present condition. It cannot automatically be used to overturn the conclusion of the original report. Over a retention period a sample can age, absorb moisture, relax under stress or undergo coating changes, all of which are functions of time and none of which mean the original testing was wrong. Reading retest data as a direct refutation of the original report is a very common misreading, and the starting point for a lot of avoidable friction. For a retest that genuinely carries comparative meaning, the preconditions are that storage conditions were controlled, that the condition of the sample can be demonstrated, and that both sides agreed beforehand on the method to be used and the rule by which the decision will be made.
Three failure scenarios with very different price tags
Scenario one. Late in the project the receiving party asks for supplementary evidence related to the sterile barrier system. The retained units the laboratory holds are the ones that were opened for inspection at the time, so they cannot be used directly. The outcome is not "pull it from storage and retest" but a full loop of new production, resterilisation, reshipment and retesting. Measured against project milestones, that time cost frequently swallows a whole submission window.
Scenario two. Retained samples were stored in the same area as samples awaiting test, and an adjacent unit was picked up for testing. The data did not match the batch that had actually been submitted, and identification plus the in-and-out log were what tracked it back. That one counts as a lucky escape, but if the labels applied at the time had been the flimsy paper kind, the only option would have been to void the data and start again.
Scenario three. The contract said nothing about a retention period, so the laboratory disposed of the samples at term under its internal rule, and several batches later the client came back asking for them. The physical items were gone. Neither side was at fault, and the project stalled all the same. The fix for this one lives entirely at the front end: write the retention period into the contract and agree a reminder window ahead of disposal.
Do not cut corners on disposal
Disposal at term needs authorisation, records and a witness, and anything containing special materials has to be handled to the corresponding requirements. The more practical point is this: give the client a reminder window before disposal so they have the chance to decide whether to extend retention or take the items back. This step adds almost no cost and heads off the scenario three situation where nobody did anything wrong and everybody suffers. The whole flow from submission through to disposal can be aligned in advance against the testing process.
Self-check list
- Was the submitted quantity prepared as test quantity plus retention quantity together, rather than counted from leftovers
- For destructive items, was an untested unit from the same batch retained, not just the tested remains
- Are sterile barrier system retained samples still unopened, with packaging untransferred
- Does every retained sample carry a dedicated number that traces both ways to the report and the test records
- Is the storage area physically separated from samples awaiting test and samples awaiting disposal, and is the identification durable
- Is the retention period written into the contract, and is there a reminder mechanism before disposal
Aligning retention policy with your project
If you are preparing a sample submission and are unsure how many units to build, which items require untested units to be retained, or how to keep packaging condition intact, send over the product construction, the test plan and the likely downstream regulatory use. We will give item-by-item retention recommendations and retention period positions and write them into the service order, so nothing gets left to "we will sort that out later". Call +86 132 4819 8029, or request a quote.